The death of a 13-year-old boy believed to have suffocated himself at his Lancashire care home this week was "almost impossible to believe", his headteacher said, as a full investigation was opened.

Mohammed Alam Naseem, known as Alam, was found dead in his bed at the home in Tockholes Road, Darwen, on Monday.

Emergency services were called to the property shortly before 12.30pm, a spokeswoman for Lancashire police said. The death is not being treated as suspicious and the coroner has been informed.

Alam's headteacher at Haslingden high school, Mark Jackson, said he was shocked to hear the "extremely sad" news. "I, and the staff I have spoken to, have found it almost impossible to believe. Everyone had taken Alam to their hearts in the 18 months he has been at the school.

"Alam was a happy, creative and confident student within our school community. He threw himself into playing an active role as soon as he joined the school – as a contestant in our 'Xmas factor' musical talent show in front of 1,000 students and later raising money for charitable causes.

"He loved to perform and his energy and charisma shone through when he entertained others. His enthusiasm, strong will and determination pervaded everything he did. His laugh was infectious, as was the kindness and friendliness he showed to those around him.

"He had a large friendship group, and was popular and liked by everyone in the school. He will be missed by all the staff and students here, and the school would like to offer our sincerest condolences and sympathies to all of his loved ones at this sad and unhappy time.

"As the school is on holiday this week, it is difficult for us to be able to support staff and pupils in the way we would like. However, we are receiving help from the county council's critical incident support team, and will be making sure that pupils and staff are cared for when they return on Monday."

Helen Denton, Lancashire county council's executive director for children and young people, said: "This is a very sad incident indeed. On behalf of the county council I would like to offer my sympathy to Alam's family, and to all those staff, teachers and other young people who lived with him and knew him.

"While we understand that there do not appear to be any suspicious circumstances surrounding this tragic death, it will of course be the subject of a full investigation, which has already begun."